The present invention relates to a toner composition for electrophotography and more specifically to a toner composition for electrophotography being excellent in both low-temperature fixing ability and offset resistance.
In electrophotography, images are obtained by forming electric latent images on a photosensitive substance by a variety of means utilizing photoconductive materials, then, the latent images are developed with a toner, followed by transferring the images onto an image support such as paper according to demand and then fixing the images with, for instance, a heating roll for fixing. A variety of resins have been investigated for use in such toners. In particular, polyester resins have been used as resins for toners which can be fixed to a transfer paper with a heating roll for fixing, because of their excellent properties such as ability for wetting the transfer paper, good compatibility with a coloring agent such as carbon black, and excellent fixing ability, when it is molten.
It is required in electrophotography that clear images be provided in a stable condition from the viewpoint of transfer of information. Recently, because the quantity of information to be handled has increased, a correspondingly faster rate of reproduction has been required. As the rate of reproduction increases, however, a great deal of heat is consumed by copying paper. Therefore, the surface temperature of the heating roll for fixing is greatly lowered in proportion to the increase in the number of copied paper. Thus, a toner is needed which does not exhibit an offset phenomenon and insufficient fixing, which has a wide range of permitted fixing temperature and which makes it possible to perform stable fixing, even when the surface temperature of the heating roll for fixing varies.
In conventional toners where a polyester resin is employed, additions such as a low molecular weight polyolefin or a partially incorporated a gel component have been used to eliminate the foregoing problems. However, the foregoing problems still have yet to be fundamentally solved, since the surface temperature of the heating roll for fixing is beyond the lower limit (low temperature fixing ability) and/or the upper limit (offset resistance) of the permitted fixing temperature of the toner.